A report conducted by University College London warned that only 30 per cent of patients involved in the early pilots were aware of the summary care record, even though all should have received letters informing them.

If the patient does nothing after receiving the letter their records will automatically be uploaded to the system. Only if they actively opt out will their records remain with their local GP.

This method of 'implied consent' was questioned in the UCL report and it was warned that it should be urgently reviewed.

The UCL report said: "Health information systems academics and ethicists have argued that implied consent (“if we don’t hear form you, we’ll upload your record”) is only informed consent (and only ethical) if there is evidence that the patient has read and understood their mail and also that they know what is on their record."

It said that there was considerable resistance from GP staff responsible for patient confidentiality, known as Caldicott Guardians.

"The fact that much of the individual resistance within GP practices has come not from IT-ignorant ‘laggards’ but from Caldicott Guardians who are generally the most information-literate members of staff and certainly the formal custodians of the practice’s data adds weight to the argument that the current consent model should be urgently reviewed," it said.

It comes as five of the ten strategic health authorities in England are starting to write to patients about uploading their data.

The Daily Telegraph highlighted the problems yesterday and dozens of readers have written to say they have had problems trying to opt out of the system.

They complained that the information packs do not contain opt out forms and they are instead directed to a national phone number or a website to download one instead.

The letters emphasise the benefits of the summary care record and imply that patient safety may be put at risk by not having one because doctors may not know the patient's current medications or allergies.

GPs in London, where letters are currently being sent to patients, are so concerned over the lack of public understanding of the care record that they have produced their own leaflets and posters for practices.

Dr Michelle Drage, chairman of the Londonwide Local Medical Committees, which represent GPs in the capital, said: "We have already been getting reports from practices seeing patients who are confused and who do not understand what the letters said.

"We will be sending further guidance out to doctors."

Dr Grant Ingrams, chairman of GP IT Committee at the British Medical Association warned that the letters looked like junk mail and so may have been thrown away or patients may not have understood them.

He said: "We should be looking at this again."

Prof Ross Anderston, professor of security engineering at Cambridge University said the consent system was 'not valid'.

He said: "Research has shown that seven out of ten people in the pilot areas were completely unaware that the summary care record existed. The basis for consent is false."

University College London are currently compiling a second report on the summary care record which is due to be presented to ministers next month.

A Department of Health spokesman said: “As well as writing to patients individually to inform them about creating a Summary Care Record, we built in an extra level of protection by asking patients permission for their records to be viewed by healthcare professionals. This is directly in response to the recommendation made by the UCL evaluation in 2008.

“The current UCL evaluation was extended to promote continued learning as Summary Care Records begin to be implemented more widely."